Valves are used to control flow in a variety of applications. In certain applications, such as power plant applications, valves, which are generally very stiff and inflexible structures, are exposed to high temperature environments that can compromise the operation of the valve. In particular, high temperatures may cause a valve stem to expand, which may lead to valve failure. For example, the expansion of the valve stem results in damage to components of the valve, such as the seat, or bending of the stem under excessive compressive stress caused by the increased length of the stem.
For valves used in high temperature environments, the internal service temperature of a valve can reach up to about 1100 degree Fahrenheit when the valve is in an open position. As a result, the valve body and most internal components of the valve are exposed to extreme heat and have filly expanded thermally, while a substantial length of the valve stem protrudes from the valve body and is thus exposed to the cooler ambient temperature. When the valve is closed, a poppet at the end of the valve stem is pushed hard against the body seat to block fluid flow. During closing, a cooler portion of the stem previously exposed to the cooler ambient exterior is now inserted from the cooler ambient exterior into the 1100 degree Fahrenheit environment and begins to thermally expand. Because there is no backlash in the drive train and the stem threads and gearing used to operate the valve stem are self-locking, the expansion of the stem must be accommodated in some manner. An uncompensated expansion of the valve stem may result in significant damage to the valve.
Prior systems for accommodating an expansion of a valve stem are implemented in the operator assembly for a valve, and can be expensive and fairly complicated to implement.
In addition, inertial effects due to opening and closing of the valve can lead to damage of the valve components absent compensation.